Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.61   4.640%   $59.2367   $59.24   $59.25   $59.20  
  Purchase #2 $102.89   12.125%   $115.3654   $115.37   $115.35   $115.40  
  Purchase #3 $54.63   13.502%   $62.0061   $62.01   $62.00   $62.00  
  Purchase #4 $85.31   13.726%   $97.0197   $97.02   $97.00   $97.00  
  Purchase #5 $42.91   3.266%   $44.3114   $44.31   $44.30   $44.30  
  Purchase #6 $17.85   11.590%   $19.9188   $19.92   $19.90   $19.90  
  Purchase #7 $105.26   12.214%   $118.1165   $118.12   $118.10   $118.10  
  7 purchase totals = $465.46       $515.9746   $515.99   $515.90   $515.90